[pjGHT]
give the information—what is the number of revolutions at which
the 85 by 92 engine gives off the 9-h.p., and also what is the total
weight of the engine. If it is merely an ordinary standard pattern
engine, then the machine is severely handicapped by carrying a lot
of unnecessary weight, and if it were equipped with a specially
designed light engine, like the Continental machines, he would
obtain far superior results.
An engine with such a short stroke as he mentions should be
quite capable of running satisfactorily at 2,50) revs, per minute,
and at that speed it should give off more than 9-b.h.p., that is
assuming that the ports and passages, &c., are properly designed
for that speed. And if 9-h.p. is all the power that is actually
required, then a still smaller engine, with consequent reduction in
weight, should do the work.
Barnes. CYLINDER.
FIRST MOTOR-DRIVEN MODEL.
[349] Enclosed you will find two photographs of a working
model monoplane, which is, I believe, the first of its kind fitted
with a petrol engine.
The machine is more or less a scale copy of the Bleriot, has an
8 ft. spread, and an overall length of 6 ft. It is fitted with one of
the Automobile Supply Co.'s J-h.p. air-cooled petrol engines,
weight ready for flight is under 15 lbs.
The
FEBRUARY 12, 1910.
PROPELLERS.
[350] Replying to F. C. Harrop's letter (268), in your issue of
the 1st inst., I enclose herewith diagrammatic sketch showing an
apparatus suitable for ascertaining the thrust of small screws. The
arrangement consists of an electric motor, R, mounted on a frame
work consisting of four straight pieces of metal on each side of the
motor. The metal pieces are pivoted at A, B, C and D, the bottom,
piece being fixed to the wooden support, E, secured to the base, F,
in such a manner that the motor can swing from right to left, and
via versd, but the frame is normally kept in position by one of the
side pieces, G, being extended downwards, and provided with a
counterweight which can be slid up or down. When at rest the
centre mark, H, at the bottom extremity of G, coincides with the
pointer, J. Different propellers which it is desired to test can be
mounted on the motor shaft, K. When the propeller is fixed in
position and the motor started, the thrust will cause G to swing into
a position out of the vertical, as indicated by the dotted line, L,
when the motor has reached the correct speed, the weight, M, is
slipped down until H again coincides with the pointer, J. The part
of G, below the pivot, C, is marked with divisions so that the exact
Mr. J. Urlwia's working model monoplane, side view. f
1^-
H
M
-
y
i
0
0
\
!
~—i.
F \
The framework has been constructed of close-grain deal through
out, and particular attention was given to the manufacture of the
ribs for the main-planes. Two hundred and fifty of these were cut
from the solid, and the best specimens selected. The planes are
single surfaced on the upper side. Rubber-proofed fabric has been
used, the fabric being fastened in the first place by drawing-pins,
and gradually stretched. • •
There are several original features in the construction of the
machine, one of which is the shock-absorber, and another the
method of tilting the main-planes to vary the angle of incidence.
The object of the model is to experiment on the subject ot
inherent stability in machines of this type.
Bletchingley. J. URLWIN.
position of the weight, M, necessary to bring G back to the vertical
under the influence of the thrust can be noted.
If an ammeter is fixed in the motor-circuit, it will indicate the
proportionate power required by different propellers to produce the
thrust indicated by the position of the weight, M, at any given speed.
An electric motor takes current exactly in proportion to the power
absorbed (the current required to run the motor light should be
deducted from each reading). The divisions on G can be arranged
to indicate the thrust in lbs. or other suitable unit.
By noting the speed, current, and position of M, and tabulating
these results, a good deal of information as to the merits of different
propellers could be obtained.
Holland Park. JAMES F, CLUNAS.
Front view of Mr. J. Urlwin's model monoplane.
114